Human leukocyte antigen antibodies and chronic rejection: from association to causation

Expression of blood group genes by mesenchymal stem cells

Incompatible blood group antigens are highly immunogenic and can cause graft rejections. Focusing on distinct carbohydrate- and protein-based membrane structures, defined by blood group antigens, we investigated human bone marrow-derived mesenchymal stem cells (MSCs) cultured in human serum. The presence of H (CD173), ABO, RhD, RhCE, RhAG, Kell, urea transporter type B (SLC14A1, previously known as JK), and Duffy antigen receptor of chemokines (DARC) was evaluated at the levels of genome, transcriptome and antigen. Fucosyltransferase-1 (FUT1), RHCE, KEL, SLC14A1 (JK) and DARC mRNA were transcribed in MSCs. FUT1 mRNA transcription was lost during differentiation. The mRNA transcription of SLC14A1 (JK) decreased during chondrogenic differentiation, while that of DARC increased during adipogenic differentiation. All MSCs synthesized SLC14A1 (JK) but no DARC protein. However, none of the protein antigens tested occurred on the surface, indicating a lack of associated protein function in the membrane. As A and B antigens are neither expressed nor adsorbed, concerns of ABO compatibility with human serum supplements during culture are alleviated. The H antigen expression by GD2dim+ MSCs identified two distinct MSC subpopulations and enabled their isolation. We hypothesize that GD2(dim+) H(+) MSCs retain a better 'stemness'. Because immunogenic blood group antigens are lacking, they cannot affect MSC engraftment in vivo, which is promising for clinical applications.

The pathology of chronic allograft dysfunction

Chronic allograft dysfunction is associated with a variety of fibrosing/sclerosing changes in the allograft. Fibrosis is multifactorial, a final pathway following varying types of injury. Using a range of diagnostic criteria, the pathologist can and should define specific lesions enabling identification of pathogenic processes affecting the allograft. Although some cases remain 'interstitial fibrosis and tubular atrophy, no specific cause', specific diagnoses can be made in most cases. Drug toxicity, bacterial or viral infection, hypertension, obstruction, recurrent or de novo renal diseases, and acute and chronic cell- and/or antibody-mediated rejection can be diagnosed in this setting. Of particular concern is a combination of persistent inflammation and fibrosis, which has repeatedly been shown to be correlated with poor graft outcomes. Identification of ongoing activity, and the stage of evolution of fibrosis/sclerosis provides important diagnostic and therapeutic information for patient management. Histological, immunohistological, ultrastructural, and molecular studies may be needed to adequately assess the kidney in the setting of chronic allograft dysfunction. Protocol biopsies may provide diagnostic insights in early stages of late graft deterioration, or even before evident dysfunction develops.

Surveillance of alloantibodies after transplantation identifies the risk of chronic rejection

The monitoring of the levels of alloantibodies following transplantation might facilitate early diagnosis of chronic rejection (CR), the leading cause of renal allograft failure. Here, we used serial alloantibody surveillance to monitor patients with preoperative positive flow cytometric crossmatch (FCXM). Sixty-nine of 308 renal transplant patients in our center had preoperative positive FCXM. Blood was collected quarterly during the first postoperative year and tested by FCXM and single antigen bead luminometry, more sensitive techniques than complement-dependent cytotoxic crossmatching. Distinct post-transplant profiles emerged and were associated with different clinical outcomes. Two-thirds of patients showed complete elimination of FCXM and solid-phase assay reactions within 1 year, had few adverse events, and a 95% 3-year graft survival. In contrast, the remaining third failed to eliminate flow FCXM or solid-phase reactions directed against HLA class I or II antibodies. The inferior graft survival (67%) with loss in this latter group was primarily due to CR. Thus, systematic assessment of longitudinal changes in alloantibody levels, either by FCXM or solid-phase assay, can help identify patients at greater risk of developing CR.

Prevention of chronic renal allograft rejection by soluble CD83

BACKGROUND

Recombinant human soluble CD83 had previously exhibited significant immunosuppressive properties that involved interference with dendritic cell maturation in both mouse and humans, inhibition of autoimmunity in mice, and induction of antigen-specific mouse cardiac allograft tolerance when used in combination with other immunosuppressive drugs. Our current research focus turned to examining the effects of peritransplant soluble CD83 (sCD83) administration on prevention of chronic renal allograft rejection.

METHODS

Fisher344-to-Lewis orthotopic rat renal transplants were performed with sequential recipient killing on postoperative days (PODs) 2, 14, and 140 to examine both the acute and chronic effects of peritransplant sCD83 treatment in rat recipients.

RESULTS

Recipients treated with sCD83 exhibited a marked decrease in IgM and IgG deposition in the graft and antidonor antibody levels in the circulation, as early as POD14 and persisting until POD140. sCD83 treatment also reduced the infiltration of T cells and monocytes into the graft tissue and inhibited intragraft expression of MyD88 and inflammatory cytokine levels during the observation period. sCD83-treated grafts demonstrated normal histology beyond POD140, including dramatic reductions in tubular atrophy and interstitial fibrosis compared with untreated recipients.

CONCLUSION

We have demonstrated that peritransplant treatment with recombinant sCD83 attenuates both innate and adaptive immune responses and leads to prevention of chronic rejection in a rat renal transplant model. Because sCD83 is of human origin, the therapeutic approach used in our rodent transplant model holds significant promise for clinical transplantation.

CD8+ T cells negatively regulate IL-4-dependent, IgG1-dominant posttransplant alloantibody production

We have previously reported that CD8(+) T cells significantly influence Ab production based on the observation that posttransplant alloantibody levels in CD8-deficient murine hepatocyte transplant recipients are markedly enhanced. However, the precise mechanisms contributing to enhanced alloantibody production in the absence of CD8(+) T cells is not understood. We hypothesized that alloactivated CD8(+) T cells inhibit Ab production by skewing toward a proinflammatory cytokine profile, whereas when these cells are absent, an anti-inflammatory cytokine profile shifts the alloimmune response toward alloantibody production. To investigate this possibility, alloantibody isotype profiles were examined in CD8-deficient and wild-type hepatocyte recipients. We found that IgG1 (IL-4-dependent isotype) was the dominant alloantibody isotype in wild-type recipients as well as in CD8-deficient recipients, although the amount of alloantibody in the latter group was substantially higher. Utilizing real-time PCR we found that CD4(+) T cells from wild-type recipients significantly upregulated IFN-γ but not IL-4 mRNA. In contrast, in the absence of CD8(+) T cells, CD4(+) T cells switched to significantly upregulate IL-4 mRNA, while IFN-γ was downregulated. IL-4 knockout mice do not produce any posttransplant alloantibody. However, adoptive transfer of wild-type CD4(+) T cells into CD8-depleted IL-4 knockout mice restores high alloantibody levels observed in CD8-depleted wild-type recipients. This suggests that IL-4-producing CD4(+) T cells are critical for posttransplant alloantibody production. Additionally, this CD8-mediated regulation of posttransplant alloantibody production is IFN-γ-dependent. Further elucidation of the mechanisms by which CD8(+) T cells influence Ab production will significantly contribute to development of therapies to manipulate humoral responses to Ag.

Acquisition of humoral transplantation tolerance upon de novo emergence of B lymphocytes

A major obstacle to transplantation tolerance is humoral immunity. In this paper, we demonstrate that the intrinsic developmental propensity of the B lymphocyte compartment for acquisition of self-tolerance can be harnessed to induce humoral unresponsiveness to transplanted alloantigens. In the current study, when transitional B cells developed in the presence of donor lymphoid cells, the mature B lymphocyte compartment failed to mount a donor-specific alloantibody response to an organ transplant--despite unrestrained acute T cell-mediated allograft rejection. Specifically, we generated an experimental system wherein a B6 strain B cell compartment developed de novo in the presence of F1 (B6xBALB/c) lymphoid cells and in a T cell-deficient setting. Following establishment of a steady-state B cell compartment, these B6 mice were transplanted with heterotopic cardiac allografts from allogeneic BALB/c donors. The mice were then inoculated with purified syngeneic B6 T cells. As expected, all cardiac allografts were acutely rejected. However, the B lymphocyte compartment of these mice was completely inert in its capacity to form a BALB/c-specific alloantibody response. Using an alloantigen-specific Ig transgenic system, we demonstrated that this profound degree of humoral tolerance was caused by clonal deletion of alloreactive specificities from the primary B cell repertoire. Thus, de novo B cell compartment development at the time of transplantation is of critical importance in recipient repertoire "remodeling" to a humoral tolerant state.

Evidence for antibody-mediated injury as a major determinant of late kidney allograft failure

BACKGROUND

Late graft failure (LGF) is believed to be the consequence of immunologic and nonimmunologic insults leading to progressive deterioration in kidney function. We studied recipients with new onset late kidney graft dysfunction (n=173) to determine the importance of C4d staining and circulating donor-specific antibody (DSA) in subsequent LGF.

METHODS

One hundred seventy-three subjects transplanted before October 1, 2005 (mean time after transplant 7.3+/-6.0 years) had a baseline serum creatinine level of 1.4+/-0.3 mg/dL before January 1, 2006 and underwent biopsy for new onset graft dysfunction after that date (mean creatinine at biopsy 2.7+/-1.6 mg/dL). Statistical analysis was based on central DSA and blinded pathology determinations.

RESULTS

Subjects were divided into four groups based on C4d and DSA: no C4d, no DSA (group A; n=74); only DSA (group B; n=31); only C4d (group C; n=28); and both C4d and DSA (group D; n=40). Among DSA+ recipients (groups B and D), group D had broader reactivity and a stronger DSA response. After 2 years, groups C and D (C4d+) were at significantly greater risk for LGF than groups A and B. Adjusting for inflammation (Banff i, t, g, and ptc scores) did not change the outcome. Local diagnosis of calcineurin inhibitor nephrotoxicity was spread across all four subgroups and did not impact risk of LGF.

CONCLUSIONS

Evidence of antibody-mediated injury (DSA or C4d) is common (57%) in patients with new onset late kidney allograft dysfunction. The risk of subsequent graft failure is significantly worse in the presence of C4d+ staining.

Identification of specificities of antibodies against human leukocyte antigens in blood donors

BACKGROUND

Transfusion-related acute lung injury (TRALI) is the leading cause of transfusion-related mortality. Blood centers are implementing TRALI risk reduction strategies based on screening apheresis donors for antibodies to human leukocyte antigens (HLA).

STUDY DESIGN AND METHODS

HLA antibody screening was performed on 7920 blood donors from the Leukocyte Antibody Prevalence Study (LAPS) using Luminex-based normalized background (NBG) cutoff ratios of 10.8 (Class I) and 6.9 (Class II). Single antigen bead (SAB) assay cutoffs of 2500 median fluorescence intensity units (Class I) and 1500 (Class II) were established based on results of two subpopulations of LAPS donors. Antibody frequencies against HLA A, B, C, DR, DQ, and DP antigens were determined for screen-reactive donors with prior pregnancies.

RESULTS

SAB reactivity for samples above our multiantigen bead NBG cutoffs was 78% for Class I and 79% for Class II. The SAB-positive rate increased among women with zero to four or more pregnancies (0.3%-15.6% Class I and 0.4%-18% Class II; p < 0.00001). The highest frequency antibodies were DR11 and B15 (4.4% of women with prior pregnancies). The majority of Class I positives contained more than five specificities. For Class II, antibody-positive women segregated into two groups: a single specificity or more than five specificities.

CONCLUSIONS

Identification of HLA antigen specificities supports pregnancy associations previously found with screening assays. The significance of particular HLA specificities for inducing TRALI is currently being evaluated in a large lookback study of recipients of high-plasma-volume components from this donor cohort.

B-lymphocyte homeostasis and BLyS-directed immunotherapy in transplantation

Current strategies for immunotherapy after transplantation are primarily T-lymphocyte directed and effectively abrogate acute rejection. However, the reality of chronic allograft rejection attests to the fact that transplantation tolerance remains an elusive goal. Donor-specific antibodies are considered the primary cause of chronic rejection. When naive, alloreactive B-cells encounter alloantigen and are activated, a resilient "sensitized" state, characterized by the presence of high-affinity antibody, is established. Here, we will delineate findings that support transient B-lymphocyte depletion therapy at the time of transplantation to preempt sensitization by eliminating alloreactive specificities from the recipient B-cell pool (ie, "repertoire remodeling"). Recent advances in our understanding of B-lymphocyte homeostasis provide novel targets for immunomodulation in transplantation. Specifically, the tumor necrosis factor-related cytokine BLyS is the dominant survival factor for "tolerance-susceptible" transitional and "preimmune" mature follicular B-cells. The transitional phenotype is the intermediate through which all newly formed B-cells pass before maturing into the follicular subset, which is responsible for mounting an alloantigen-specific antibody response. Systemic BLyS levels dictate the stringency of negative selection during peripheral B-cell repertoire development. Thus, targeting BLyS will likely provide an opportunity for repertoire-directed therapy to eliminate alloreactive B-cell specificities in transplant recipients, a requirement for the achievement of humoral tolerance and prevention of chronic rejection. In this review, the fundamentals of preimmune B-cell selection, homeostasis, and activation will be described. Furthermore, new and current B-lymphocyte-directed therapy for antibody-mediated rejection and the highly sensitized state will be discussed. Overall, our objective is to propose a rational approach for induction of humoral transplantation tolerance by remodeling the primary B-cell repertoire of the allograft recipient.

Prevention trumps treatment of antibody-mediated transplant rejection

Belying the spectacular success of solid organ transplantation and improvements in immunosuppressive therapy is the reality that long-term graft survival rates remain relatively unchanged, in large part due to chronic and insidious alloantibody-mediated graft injury. Half of heart transplant recipients develop chronic rejection within 10 years - a daunting statistic, particularly for young patients expecting to achieve longevity by enduring the rigors of a transplant. The current immunosuppressive pharmacopeia is relatively ineffective in preventing late alloantibody-associated chronic rejection. In this issue of the JCI, Kelishadi et al. report that preemptive deletion of B cells prior to heart transplantation in cynomolgus monkeys, in addition to conventional posttransplant immunosuppressive therapy with cyclosporine, markedly attenuated not only acute graft rejection but also alloantibody elaboration and chronic graft rejection. The success of this preemptive strike implies a central role for B cells in graft rejection, and this approach may help to delay or prevent chronic rejection after solid organ transplantation.

Preemptive CD20+ B cell depletion attenuates cardiac allograft vasculopathy in cyclosporine-treated monkeys

Chronic rejection currently limits the long-term efficacy of clinical transplantation. Although B cells have recently been shown to play a pivotal role in the induction of alloimmunity and are being targeted in other transplant contexts, the efficacy of preemptive B cell depletion to modulate alloimmunity or attenuate cardiac allograft vasculopathy (CAV) (classic chronic rejection lesions found in transplanted hearts) in a translational model has not previously been described. We report here that the CD20-specific antibody (alphaCD20) rituximab depleted CD20+ B cells in peripheral blood, secondary lymphoid organs, and the graft in cynomolgus monkey recipients of heterotopic cardiac allografts. Furthermore, CD20+ B cell depletion therapy combined with the calcineurin inhibitor cyclosporine A (CsA) prolonged median primary graft survival relative to treatment with alphaCD20 or CsA alone. In animals treated with both alphaCD20 and CsA that achieved efficient B cell depletion, alloantibody production was substantially inhibited and the CAV severity score was markedly reduced. We conclude therefore that efficient preemptive depletion of CD20+ B cells is effective in a preclinical model to modulate pathogenic alloimmunity and to attenuate chronic rejection when used in conjunction with a conventional clinical immunosuppressant. This study suggests that use of this treatment combination may improve the efficacy of transplantation in the clinic.

HLA-E monoclonal antibodies recognize shared peptide sequences on classical HLA class Ia: relevance to human natural HLA antibodies

The non-classical HLA-Ib molecule, HLA-E share several peptide sequence similarities with the heavy chains of classical HLA class Ia (-B and -C) molecules. Therefore, the antibodies to HLA-E, that recognize shared sequences, may bind to HLA-Ia alleles. This hypothesis is tested by examining the affinity of HLA-E monoclonal antibodies (HLA-E-MAbs) to HLA-Ia molecules and by inhibiting the antibody binding to both HLA-E and HLA-Ia with the shared peptide sequence(s). Single recombinant HLA molecule-coated beads are used for antibody binding. The antibody binding is evaluated by measuring mean fluorescence index [MFI] with Luminex multiplex flow-cytometric technology. The peptide-inhibition experiments are carried out with synthetic shared peptides, most prevalent to HLA-E and HLA-Ia alleles. The number of HLA-Ia alleles recognized by the HLA-E-MAbs varies with the density of the antigen (quantity of antigen-coated beads) and dilution of MAb. Binding of HLA-E-MAbs to beta2 microglobulin (beta(2)m)-free HLA-Ia antigens confirms the location of the epitopes on the heavy chain (HC) of the antigens. Strikingly, the nature of alleles of HLA-Ia recognized by different HLA-E-MAbs is identical. The binding of HLA-E-MAbs to the HLA-Ia is inhibited dosimetrically by the adjacent peptides, (115)QFAYDGKDY(123) and (137)DTAAQI(142), but not by (126)LNEDLRSWTA(135), another closer shared peptide sequence. The inhibitory peptide sequences in HLA-E are at the alpha2-helix terminal facing beta(2)m. The HLA-Ia alleles recognized by HLA-E-MAb (e.g., MEM-E/02) are similar to those recognized by the natural anti-HLA antibodies found in the sera of healthy non-alloimmunized males. This study postulates that some, if not all, of the natural HLA-Ia antibodies seen in healthy males could be anti-HLA-E antibodies cross-reacting with HLA-Ia alleles.

Histopathologic clusters differentiate subgroups within the nonspecific diagnoses of CAN or CR: preliminary data from the DeKAF study

The nonspecific diagnoses 'chronic rejection''CAN', or 'IF/TA' suggest neither identifiable pathophysiologic mechanisms nor possible treatments. As a first step to developing a more useful taxonomy for causes of new-onset late kidney allograft dysfunction, we used cluster analysis of individual Banff score components to define subgroups. In this multicenter study, eligibility included being transplanted prior to October 1, 2005, having a 'baseline' serum creatinine < or =2.0 mg/dL before January 1, 2006, and subsequently developing deterioration of graft function leading to a biopsy. Mean time from transplant to biopsy was 7.5 +/- 6.1 years. Of the 265 biopsies (all with blinded central pathology interpretation), 240 grouped into six large (n > 13) clusters. There were no major differences between clusters in recipient demographics. The actuarial postbiopsy graft survival varied by cluster (p = 0.002). CAN and CNI toxicity were common diagnoses in each cluster (and did not differentiate clusters). Similarly, C4d and presence of donor specific antibody were frequently observed across clusters. We conclude that for recipients with new-onset late graft dysfunction, cluster analysis of Banff scores distinguishes meaningful subgroups with differing outcomes.

Predicting HLA class I alloantigen immunogenicity from the number and physiochemical properties of amino acid polymorphisms

BACKGROUND

Knowledge of the human leukocyte antigen (HLA) amino acid (AA) sequence combined with crystallographic structural data may enable prediction of the relative immunogenicity of individual donor/recipient HLA mismatches.

METHODS

Multiple sera from 32 highly sensitized patients awaiting kidney transplantation were screened using Luminex/single-antigen beads to determine the HLA-specific antibody levels against mismatched HLA class I specificities. A computer program was developed to allow intralocus and interlocus comparison of mismatched HLA-A and -B specificities with corresponding recipient HLA class I type, and to determine the number, position, and physiochemical disparity (hydrophobicity and electrostatic charge) of polymorphic AA.

RESULTS

HLA-specific antibody was detected against 1666 (85%) of the 1964 mismatched HLA specificities evaluated, with a close correlation between increasing number of AA polymorphisms and the presence and magnitude of the alloantibody response (P<0.0001). Hydrophobicity and electrostatic charge disparity scores were independent predictors of alloantibody production (adjusted P=0.0009 and P=0.0005, respectively). Mismatched specificities with physiochemical scores within the first decile of the scale led to weak alloantibody responses (median fluorescence intensity 2330), whereas those with scores above the sixth decile led to strong alloantibody production (median fluorescence intensity >10,000).

CONCLUSION

Differences in AA number, hydrophobicity, and electrostatic charge between HLA class I specificities enable prediction of donor HLA class I types with low immunogenicity for a given recipient.

HLA class I antibodies provoke graft arteriosclerosis in human arteries transplanted into SCID/beige mice

Antibodies toward HLA class I and/or MICA are commonly observed in transplanted patients suffering from allograft arteriosclerosis, also called chronic vascular rejection (CVR). The relative importance of cellular versus humoral alloreactivity for CVR is still disputed. We demonstrate that antibodies toward HLA class I provoke lesions typical for CVR in human arteries in vivo in the absence of cellular immunity. To show this, we grafted segments of human mesenteric arteries from 8 deceased organ donors into 36 immunodeficient SCID/beige mice in the infrarenal aortic position. Three mice died postoperatively. The remaining 33 mice received weekly i.v. injections of either a monoclonal antibody toward HLA class I, toward MICA or an irrelevant monoclonal antibody. At sacrifice after 6 weeks, mice receiving the HLA antibody showed a significant neointimal thickening in the grafted artery due to smooth muscle cell (SMC) proliferation while control mice receiving anti-MICA or irrelevant antibody showed little or no thickening. Whereas antibodies toward HLA class I were mitogenic to SMC in vitro, those directed toward MICA did not have any effect. Humoral alloreactivity toward HLA may thus play a causal role for the development of CVR and this opens new possibilities for the treatment of CVR.

B-cell tolerance in transplantation: is repertoire remodeling the answer?

T lymphocytes are the primary targets of immunotherapy in clinical transplantation; however, B lymphocytes and their secreted alloantibodies are also highly detrimental to the allograft. Therefore, the achievement of sustained organ transplant survival will likely require the induction of B-lymphocyte tolerance. During development, acquisition of B-cell tolerance to self-antigens relies on clonal deletion in the early stages of B-cell compartment ontogeny. We contend that this mechanism should be recapitulated in the setting of alloantigens and organ transplantation to eliminate the alloreactive B-cell subset from the recipient. Clinically feasible targets of B-cell-directed immunotherapy, such as CD20 and B-lymphocyte stimulator (BLyS), should drive upcoming clinical trials aimed at remodeling the recipient B-cell repertoire.

Anti-HLA antibodies posttransplantation in children: do we know what it means?

OBJECTIVE

Anti-HLA antibodies posttransplantation are associated with the appearance of acute and chronic rejection. The goal of this study was to determine the association between the presence of anti-HLA antibodies posttransplantation in children and the clinical outcome.

PATIENTS AND METHODS

We studied the presence and the level of class I and II anti-HLA antibodies by microbead technology (Luminex) in 32 children after kidney transplantation; 87% underwent a first transplantation. Their mean age was 13.9 +/- 2.52 years. When anti-HLA was positive, 60% of children showed an increase in creatinine within the previous 3 months. The statistical analysis was performed with the SPSS 9.0 program.

RESULTS

Only 4/32 children displayed class I anti-HLA antibodies at low levels (5-7.2) and 43% class II anti-HLA antibodies (level: 5-308). We did not observe an association between the presence of antibodies and age, sex, type of donor, immunosuppression, hypertension, proteinuria, time from transplantation, or reason to evaluate antibodies; 37.5% showed good graft function. The presence of anti-HLA antibodies posttransplantation was associated with retransplantations and with the percentage of antibodies by panel-reactive antibodies. There was trend towards an association with a previous acute rejection episode (P = .072); 62.5% of children with C4d-positive biopsies displayed anti-HLA antibodies vs 20% of those who were C4d-negative (P = .088). Graft survival was 100%.

CONCLUSIONS

The presence of anti-HLA antibodies posttransplantation was influenced by pretransplantation factors-previous level of anti-HLA antibodies, retransplantation, DR matching- and also by posttransplantation factors, such as the occurrence of an acute rejection episode.

Binding of anti-HLA class I antibody to endothelial cells produce an inflammatory cytokine secretory pattern

Current methods are inadequate for the diagnosis of early chronic allograft rejection. The goal of this study was to determine whether ligation of anti-HLA antibodies to endothelial cells is associated with a distinctive cytokine secretory pattern. Human iliac artery endothelial cells (HIAEC) cultured in vitro were incubated with w6/32, an anti-HLA class I mAb. Culture supernatants collected daily for up to 4 days were tested for secretion of 13 cytokines using a multiplexed fluorescent microsphere immunoassay. Culture of HIAEC with medium containing mAb w6/32 supported the growth of HIAEC during the 4-day study period. Levels of the pro-inflammatory cytokines IL-1beta, IL-6, IL-8, and TNF-alpha became significantly increased in supernatants of HIAEC incubated with the mAb w6/32. We conclude that ligation of anti-HLA class I antibodies to HLA class I antigens in endothelial cells initiates an acute inflammatory process and detecting an inflammatory cytokine secretory pattern might be useful to diagnose sub-clinical chronic allograft rejection.

Abrogation of anti-HLA antibodies via proteasome inhibition

BACKGROUND

Current treatments for autoantibody-mediated diseases (i.e., systemic lupus erythematosus) and alloantibodies (in transplant) are minimally effective. Although they deplete naïve B cells, plasmablasts, and transiently reduce antibody concentrations, they are minimally effective against long-lived, antibody-producing plasma cells. In transplantation, plasma cells produce antibodies directed against human leukocyte antigen (HLA) antigens causing poor allograft survival. We report the first clinical experience with a plasma cell depleting therapy, bortezomib, to abrogate anti-HLA antibodies in transplantation (outside of rejection) in an attempt to improve long-term allograft survival.

METHODS

Eleven patients with anti-HLA alloantibodies were treated with bortezomib. All patients underwent plasmapheresis to aid in removal of antibodies and to determine the effect of bortezomib. Serial measurements of anti-HLA antibody levels were conducted weekly by single antigen bead on Luminex platform.

RESULTS

Bortezomib treatment elicited substantial reduction in both donor-specific antibody (DSA) and non-DSA levels. Antibodies were directed against DSA in 8 of 11 cases. Mean time to antibody appearance was 2 months posttransplant. Within 22 days (median) from treatment initiation, 9 of 11 patients' antibody levels dropped to less than 1000 mean fluorescence intensity. Of two patients without successful depletion, all had peak mean fluorescence intensity more than 10,000. At a mean follow-up of approximately 4 months posttreatment, all patients have stable graft function. Minimal transient side effects were noticed with bortezomib in the form of gastrointestinal toxicity, thrombocytopenia, and paresthesias.

CONCLUSIONS

Bortezomib therapy effectively abrogates anti-HLA antibodies. Hence, removal of antibodies, by proteasome inhibition, represents a new treatment strategy for transplantation and may have benefit in autoimmune-related disease.

The role of causal criteria in causal inferences: Bradford Hill's "aspects of association"

As noted by Wesley Salmon and many others, causal concepts are ubiquitous in every branch of theoretical science, in the practical disciplines and in everyday life. In the theoretical and practical sciences especially, people often base claims about causal relations on applications of statistical methods to data. However, the source and type of data place important constraints on the choice of statistical methods as well as on the warrant attributed to the causal claims based on the use of such methods. For example, much of the data used by people interested in making causal claims come from non-experimental, observational studies in which random allocations to treatment and control groups are not present. Thus, one of the most important problems in the social and health sciences concerns making justified causal inferences using non-experimental, observational data. In this paper, I examine one method of justifying such inferences that is especially widespread in epidemiology and the health sciences generally - the use of causal criteria. I argue that while the use of causal criteria is not appropriate for either deductive or inductive inferences, they do have an important role to play in inferences to the best explanation. As such, causal criteria, exemplified by what Bradford Hill referred to as "aspects of [statistical] associations", have an indispensible part to play in the goal of making justified causal claims.

Detection of immunoglobulin G human leukocyte antigen-specific alloantibodies in renal transplant patients using single-antigen-beads is compromised by the presence of immunoglobulin M human leukocyte antigen-specific alloantibodies

BACKGROUND

Luminex-based single-antigen human leukocyte antigen (HLA) antibody detection beads (SAB) are a major advance for the characterization of HLA-specific antibodies but their clinical utility is limited unless the analysis is performed and interpreted optimally. Here, we identify problems encountered in routine monitoring of antibody levels that may give rise to misleading results, and describe how these can be overcome to provide more meaningful clinical information.

METHODS AND RESULTS

HLA class I specific antibody-binding levels were determined using SAB in the sera of 42 highly sensitized patients awaiting renal transplantation. Normalization of the results against the HLA class I specific monoclonal antibody W6/32 overcame the problems caused by variation in antigen density on SAB and also suggested the presence of alloantibodies directed against multiple HLA class I epitopes of a given specificity. Routine analysis using undiluted sera gave an incomplete assessment of antibody levels. On serum dilution, three patterns of antibody binding became apparent: most sera showed a sequential reduction in immunoglobulin G (IgG) binding levels but several sera displayed antibody binding which remained unchanged (suggesting antigen saturation) or increased IgG binding on serum dilution (suggesting inhibition of IgG binding using neat serum). The presence of immunoglobulin M (IgM) HLA-specific antibodies in sera correlated with inhibition of IgG antibody binding for the corresponding specificity and treatment of sera with dithiothreitol to eliminate IgM HLA-specific blocking antibodies restored maximum IgG antibody binding levels.

CONCLUSION

When using SAB to monitor HLA-specific antibody binding levels, sera should be pretreated with dithiothreitol to eliminate blocking IgM HLA-specific antibodies that may mask clinically relevant allosensitization.

Back to the future: application of contemporary technology to long-standing questions about the clinical relevance of human leukocyte antigen-specific alloantibodies in renal transplantation

Luminex technology allows the accurate identification of human leukocyte antigen (HLA) class I and class II-specific antibodies at levels below the threshold detectable by either conventional complement-dependent lymphocytotoxicity or flow cytometry. The technology enables the analysis of complex antibody profiles in sensitized patients and gives improved definition of acceptable and unacceptable HLA specificities to guide donor kidney allocation. This helps to facilitate virtual cross-matching and avoid inappropriate shipping of kidneys for incompatible patients in distant centers. Luminex allows the cause of a positive cross-match test to be determined in a clinically relevant time scale and, when used in conjunction with lymphocytotoxic and flow cytometric cross-matching, it provides an assessment of the level of immunological risk in patients being considered as potential recipients for a particular donor kidney. Information is now emerging to enable the full clinical potential of Luminex to be realized.

Monitoring after renal transplantation: recommendations and caveats

This commentary discusses the strengths and weaknesses of a recent study reported by Kobayashi and colleagues, in which paired serum samples from 297 renal transplant recipients who underwent transplantation between December 1972 and September 2004 were tested for the presence of human leukocyte antigen (HLA) antibody at two discrete time points following surgery (2004 and 2006). Urine samples collected on the same day as the serum samples, were also measured for urinary protein levels. The results of the study suggest that patients with a positive change in HLA antibody status in the post-transplantation period (i.e. from negative to positive) plus a positive urine protein test were at increased risk of developing graft dysfunction (i.e. increased serum creatinine level). Solely on the basis of these data, the authors advocate that patients should be monitored annually for de novo production of HLA antibodies and for an increased urinary protein level by use of simple and cost-effective approaches to assess the risk of graft dysfunction or failure. While the proposal is an intriguing one, this commentary identifies several issues and limitations regarding post-transplantation monitoring that should be considered.